1. Field of the Invention
The present invention relates generally to ink-jet printing and, more specifically to an ink-jet pen carriage assembly having a torsional deflection control pen latching subsystem for increasing stiffness and maintaining accurate pen-to-paper alignment.
2. Description of Related Art
The art of ink-jet technology is relatively well developed. Commercial products such as computer printers, graphics plotters, copiers, and facsimile machines employ ink-jet technology for producing hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions. Ink-jet devices are also described by W. J. Lloyd and H. T. Taub in Output Hardcopy [sic] Devices, chapter 13 (Ed. R. C. Durbeck and S. Sherr, Academic Press, San Diego, 1988).
FIG. 1 depicts a hard copy apparatus, in this exemplary embodiment a computer peripheral, ink-jet printer, 101. A housing 103 encloses the electrical and mechanical operating mechanisms of the printer 101. Operation is administrated by an electronic controller 102 (usually a microprocessor or application specific integrated circuit ("ASIC") controlled printed circuit board) connected by appropriate cabling to a computer (not shown). It is well known to program and execute imaging, printing, print media handling, control functions and logic with firmware or software instructions for conventional or general purpose microprocessors or with ASIC's. Cut-sheet print media 105, loaded by the end-user onto an input tray 120, is fed by a suitable paper-path transport mechanism (not shown) to an internal printing station, or "print zone," 107 where graphical images or alphanumeric text is created. A carriage 109, mounted on a slider 111, scans the print medium. [Stationary, page-wide, ink-jet printhead arrays are also known in the art; page-size printhead arrays are contemplated.] An encoder subsystem 113, 114 is provided for keeping track of the position of the carriage 109 at any given time. A set of individual ink-jet pens, or print cartridges, 115X is mounted in the carriage 109 (described in more detail hereinafter with respect to FIG. 2B). Generally, in a full color system, inks for the subtractive primary colors, cyan, yellow, magenta (X=C, Y, or M) and true black (X=K) are provided; in some implementations an ink-fixer chemical (X=F) is also used. An associated set of replaceable or refillable ink reservoirs 117X is coupled to the pen set by ink conduits 119. Once a printed page is completed, the print medium is ejected onto an output tray 121. The carriage scanning axis is conventionally designated the x-axis, the print media transit axis is designated the y-axis, and the printhead firing direction is designated the z-axis.
For convenience of describing the ink-jet technology and the present invention, all types of print media are referred to simply as "paper," all compositions of colorants are referred to simply as "ink," ink-jet writing instruments are referred to as "pens" or "cartridges," and all types of hard copy apparatus are referred to simply as a "printer." No limitation on the scope of invention is intended nor should any be implied.
In essence, the ink-jet printing process involves digitized dot-matrix manipulation of drops of ink ejected from an ink-jet printhead onto an adjacent paper. The printhead generally consists of drop generator mechanisms and a number of columns of ink drop firing nozzles. Each column or selected subset (referred to in the art as a "primitive") of nozzles selectively fires ink droplets (typically each being only a few picoliters in liquid volume) that are used to create a predetermined print matrix of dots on the adjacently positioned paper as the pen is scanned across the media. A given nozzle of the printhead is used to address a given matrix column print position on the paper (referred to as a picture element, or "pixel"). Horizontal positions, matrix pixel rows, on the paper are addressed by repeatedly firing a given nozzle at matrix row print positions as the pen is scanned. Thus, a single sweep scan of the pen across the paper can print a swath of tens of thousands of dots. The paper is stepped to permit a series of contiguous swaths. Complex digital dot matrix manipulation is used to form alphanumeric characters, graphical images, and even photographic reproductions from the ink drops.
In the state of the art, the nominal printhead-to-paper spacing is about one millimeter. Printer designers attempt to reduce pen-to-paper spacing as a means of improving print quality. However, carriage assembly torsional deflections can cause each printhead face, or "nozzle plate," to be off-kilter, limiting the attempt to narrow the gap between the printhead and the paper. As illustrated in FIG. 2, a pitch angle of the printhead relative to the plane of the paper in the printing zone is referred to as theta-x (.theta.x), a roll angle is referred to as theta-y (.theta.y), and printhead yaw is referred to as theta-z (.theta.z). Any static or dynamic deflections during printing operations can result in dot placement errors and undesirable artifacts in the print.
Moreover, the problem becomes more complex when more pens are added to the printer design to accommodate higher print quality demands such as for very high resolution photographic reproductions where the ink-jet print is indistinguishable from a photolab darkroom developer process photograph, or multi-printhead, staggered, printhead array carriages for improving throughput. The larger the pen carriage, the greater the problem.
Most attempts to solve the problem focus on creating a more stable base platform for the hard copy apparatus as a whole. Such solutions often result in the use of heavier, more expensive, manufacturing materials or designs having a larger work space footprint.
Moreover, manufacturing tolerances allowed in springs, pen body datums, and the like parts of the assembly, can result in variations in torsional deflections in the carriage from assembly-to-assembly. Thus, another solution is required.
Other methods and apparatus are designed to stabilize the printhead alignment focus on the pen-to-bay interface mechanisms; see e.g., U.S. patent application Ser. No. 08/878,489 by common assignee Williams, et al. for an INKJET PEN ALIGNMENT MECHANISM AND METHOD, or U.S. patent application U.S. Ser. No. 09/431,712 by common assignor Williams, et al. for a DATUM STRUCTURE FOR COMPACT PRINT CARTRIDGE, or U.S. patent application Ser. No. 09/431,711 by Heiles et al. for a UNITARY LATCHING DEVICE FOR SECURE POSITIONING OF PRINT CARTRIDGE(S) DURING PRINTING, PRIMING AND REPLENISHMENT (each assigned to the common assignee herein and incorporated herein by reference).
Therefore, there is a need for simplified mechanisms to reduce torsional deflections in ink-jet printhead carriage assemblies.